Actuatable occupant restraining systems for use in vehicles are known in the art. Such restraining systems may include one or more collision sensing devices for sensing vehicle crash acceleration (vehicle deceleration during the crash event). Air bag restraining systems include an electrically actuatable igniter, referred to as a squib. When the collision sensing device senses a deployment crash event and provides a signal indicative thereof, an electrical current of sufficient magnitude and duration is passed through the squib to ignite the squib. When ignited, the squib initiates the flow of inflation fluid into an air bag from a source of inflation fluid, as is known in the art.
A known type of collision sensing device used in actuatable occupant restraining systems is mechanical in nature. Still other known types of collision sensing devices include an electrical transducer, such as an accelerometer, for sensing vehicle crash acceleration. Actuatable restraining systems using an accelerometer as a crash or collision sensor further include circuitry, e.g., a controller such as a microcomputer, for monitoring and analyzing the output of the accelerometer. The controller performs a crash algorithm using the accelerometer output signal for discriminating between a deployment crash event and a non-deployment crash event. When a deployment crash event is determined to be occurring, the restraining device is actuated, e.g., an air bag is deployed.
One particular type of occupant restraining system known in the art is a multi-stage occupant restraining system that includes more than one actuatable stage associated with a single air bag. In a multi-stage air bag restraining system, air bag inflation is the result of the control of a multi-stage inflator. Such multi-stage air bag systems may have two or more separate sources of inflation fluid controlled by actuation of individual squibs associated with the same air bag. Control arrangements control the actuation of the multiple stages based on, for example, a timing function between the first actuation and the second actuation. A problem may arise in determining the beginning of the crash event to start the timing process. False starts (and, in turn, false endings) could occur due to signals being generated that are the result of road noise and not a crash event.
U.S. Pat. No. 6,549,836 to Yeh et al. discloses a method and apparatus for controlling an actuatable occupant restraining device having a plurality of actuatable stages. The apparatus includes a crash sensor for sensing crash acceleration and provides a crash acceleration signal indicative thereof. A controller determines a velocity value and a displacement value from the crash acceleration signal. A side impact sensor and side impact crash event circuit determines if a side impact crash event is occurring. If a side impact crash event is occurring, the threshold values of the immunity box are adjusted.